The present invention relates generally to a measurement system including a smart sensor having data uniquely characterizing the sensor stored in a memory local to the sensor, and more particularly to a measurement system including a communications interface for use with a smart sensor.
Many applications require accurate information about a property of a given environment, such as temperature, pressure, relative humidity, etc. A sensor in contact with an environment to be sensed, for example, can convey an electrical signal indicative of the temperature, e.g., in the environment to an indicating instrument. The indicating instrument converts the electrical signal into a temperature value for display or other output indicative of that temperature. Unfortunately, however, some temperature sensors do not provide acceptably accurate temperature readings because the sensors and/or the instruments are not adequately calibrated for use with one another.
Each sensor has unique operating characteristics that the indicating instrument must take into account to provide an accurate interpretation of the signal from the sensor. Smart sensors store this data in a memory local to the sensor. The smart sensor is connected to an input/output communications port in the indicating instrument. The communications port allows the indicating instrument to send and receive data and instructions, such as requesting the characterizing data from the sensor""s memory, receiving calibration settings or outputting data, such as a temperature reading. The indicating instrument can thus be connected to an input or output device other than the smart sensor through the communications port, including a printer, a computer, a display, a keyboard, a mouse, etc. When the smart sensor is connected to the communications port, the sensor can communicate an analog signal indicative of the temperature and can communicate digitally between the indicating instrument and the memory of the smart sensor. The indicating instrument then analyzes the analog signal from the smart sensor in view of the characterizing data and outputs a value more accurately representative of the temperature.
The smart sensor and the indicating instrument generally have a predetermined relationship for communicating the characterizing data from the sensor to the instrument. The characterizing data is used by the instrument to adjust the calculated temperature value to provide a more accurate temperature reading. In a number of applications no predetermined relationship exists, particularly when the sensor manufacturer is not the instrument manufacturer. For example, the characterizing data may be in a different format (columns instead of rows, for example), have different data (such as the sensor manufacturer""s serial number) and/or may incorporate offset functions that may or may not be expected to be compensated for by the manufacturer of the indicating instrument. Consequently, some sensors are incompatible with certain indicating instruments.
Additionally, sensors generally degrade over time and must be replaced periodically, particularly when the sensor is used in a harsh environment. In contrast, indicating instruments generally last for a relatively long time. Since the indicating instrument usually is much more expensive than the sensor, it is desirable to replace the sensor while continuing to use the indicating instrument. Because the replacement sensor must be compatible with the indicating instrument for accurate operation, the indicating instrument manufacturer generally also must be the manufacturer of the selected replacement sensor. Unfortunately, that manufacturer may not offer the best performing or most attractively priced sensor for a given application.
The present invention provides a sensing system that includes a smart sensor, an indicating instrument, and a smart interface device in communication with the smart sensor and the indicating instrument. The interface device advantageously allows a smart sensor to be used with any indicating instrument. The interface device can be preprogrammed to receive data characterizing the sensor, to develop calibration data based on the characterizing data, and to communicate the calibration data to the indicating instrument. The indicating instrument uses the calibration data to output a more accurate temperature reading. In effect, the interface device acts as a translator between the smart sensor and the indicating instrument. Thus a purchaser of a replacement smart sensor is not limited by the manufacturer of the indicating instrument with which it will be used.
More specifically, the present invention includes a system for providing an indication of an environmental property, such as temperature. Such a system includes an indicating instrument, a smart sensor and a programmable interface device. The smart sensor includes a sensor unit operable to sense the environmental property and a local memory unit with characterizing data stored therein. The sensor unit may be a temperature sensor, such as a resistance temperature device or a thermocouple. The characterizing data in the memory unit includes data characterizing the operation of the sensor unit.
The memory unit of the smart sensor is connected to the interface device by a first communication link, such as a wire, for communicating the characterizing data to the interface device. The sensor unit of the smart sensor is connected to the indicating instrument either directly or via the interface device by a second communication link for communicating to the indicating instrument a signal indicative of a sensed property. The indicating instrument is connected to the interface device by a third communications link for communicating to the interface device an estimated property value determined from the sensed property signal.
The interface device includes means for determining calibration data based on the characterizing data, including means for determining the calibration data based on the characterizing data and the estimated property value. The means for determining the calibration data may include a processor and a memory unit. The memory unit of the interface device may have software instructions for communicating with the smart sensor and the indicating instrument, or for determining the calibration data, such as a calibration offset. The memory unit may be in the form of an electrically erasable programmable read-only memory.
The indicating instrument includes means for determining indicated property data. The indicating instrument may include a processor. The indicating instrument processor determines the sensed property value based on the sensed property signal from the sensor unit. The indicating instrument processor also determines the indicated property data based on the estimated property value and the calibration data. In particular, the indicating instrument processor may be operable to determine the indicated property data by adding a calibration offset to the estimated property value.
The present invention also includes a method comprising the steps of (a) connecting an interface device between a smart sensor and an indicating instrument; (b) transmitting a sensed property signal from the smart sensor to the indicating instrument; (c) determining an estimated property value based on the sensed property signal; (d) transmitting the estimated property value to the interface device; transmitting characterizing data to the interface device including data characterizing the operation of the smart sensor; (e) determining calibration data from the estimated property value and the characterizing data; and (f) determining an indicated property value based on the estimated property value and the calibration data. The method may further include the steps of transmitting sensed property data from a sensor unit of the smart sensor to the indicating instrument, determining a calibration offset, and algebraically adding the calibration offset to the estimated property value and displaying the indicated property value.
The foregoing and other features of the invention are hereinafter fully described and particularly pointed out in the claims, the following description and annexed drawings setting forth in detail a certain illustrative embodiment of the invention, this embodiment being indicative, however, of but one of the various ways in which the principles of the invention may be employed.